TELECOM Digest OnLine - Sorted: Re: Invalid Number Tones

Re: Invalid Number Tones

DevilsPGD (
Wed, 02 Feb 2005 01:38:12 -0700

In message <> L. Hao
<> wrote:

> I need to design an algorithm to detect call progress. For example, it
> needs to figure out whether the call hits a live person, an answering
> machine, a fax machine, and etc. But among all these things, I am
> having trouble finding the spec for this so-called invalid
> number. When you dial an invalid number, you normally get a tone
> followed by " the number you just dialed ...". Can anyone tell me where
> I can find the spec for this tone? Or better yet, if anyone can share
> his/her methods of detecting it, it'd be great.

In general, get a digital line (ISDN or up) and you'll get accurate
dialing information. Beyond that, I don't believe that the tones are
reliable or consistent anymore.

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